This invention relates to an ultrasonic operating apparatus and a control method for driving energy therefor, and more particularly to a driving unit for driving an ultrasonic vibrator for use in an ultrasonic operating apparatus or the like in which a medical operation is carried out by transmitting a vibration of an ultrasonic vibrator to a probe, and a control method for driving energy therefor.
In surgery operation, an endoscope has been widely used, for observing a viscus in the celom by inserting its narrow insertion portion therein or as required, and carrying out a diagnostic procedure using a treatment tool inserted in a treatment tool channel of the endoscope.
As for the treatment tool inserted into the treatment tool channel of the endoscope, various types thereof are used depending on a patient and purpose. In recent years, an ultrasonic operating apparatus for carrying out a procedure using an ultrasonic vibration has been used. As the ultrasonic operating apparatus, for example, a surgery ultrasonic knife has been well known, which comprises an ultrasonic vibrator (ultrasonic converter) like, for example, Langevin type vibrator, a probe fit to this ultrasonic vibrator for transmitting a vibration to a distal end thereof and a driving unit for vibrating the ultrasonic vibrator. Some type of the ultrasonic operating apparatus using the aforementioned art recently developed is capable of incision, homostasis, and coagulation.
Generally, a vibration amplitude of the distal end of the probe is proportional to a current for driving the ultrasonic vibrator. The driving unit supplies the ultrasonic vibrator with a current necessary for this vibration amplitude.
However, the impedance of an ultrasonic vibrator actually ultrasonically vibrated changes depending on a load condition applied to each ultrasonic vibrator and each probe. Therefore, to maintain a stable vibration amplitude regardless of a load change in the ultrasonic vibrator, such a driving unit for executing a constant current drive to maintain a current supplied to the ultrasonic vibrator on a constant level has been known.
Here assuming that the impedance of the ultrasonic vibrator is Z, a current for executing the constant current drive is I and a voltage applied to the ultrasonic vibrator by a driving unit for executing the constant current drive is V, the following expression is established. EQU Z=V/I or V=IZ (1)
As evident from the expression (1), to drive the ultrasonic vibrator under a constant current, such a requirement is satisfied if a voltage V depending on a change in the impedance Z of the ultrasonic vibrator is applied to the ultrasonic vibrator.
Further, to vibrate the ultrasonic vibrator effectively, it is desired to frequency-drive the ultrasonic vibrator at its resonance point. Therefore, a phase lock loop (PLL) control method in which the resonance point is tracked according to the phase of the current I and voltage V applied to the ultrasonic vibrator has been well known in the conventional art.
On the other hand, miniaturization of a medical apparatus has been progressed in the medical operating field so that the aforementioned ultrasonic driving unit is downsized and its output capacity becomes the smallest level.
If under such a condition, the electrical characteristic of the ultrasonic vibrator changes remarkably, for example the impedance rises remarkably, its applied load exceeds a voltage capacity which can be applied to the ultrasonic vibrator from the driving unit, so that the constant current drive for the ultrasonic vibrator is disabled.
As a result, as evident from the expression (1), a current value supplied to the ultrasonic vibrator drops. Therefore, there occurs a fault in which the ultrasonic vibrator and probe are vibrated at a vibration amplitude lower than a preferred one.
On the other hand, if the impedance of the ultrasonic vibrator drops remarkably, a voltage detected in the driving unit also drops, disabling the PLL control. As a result, there occurs a disadvantage in which its loss is converted to heat or the ultrasonic vibrator and probe are deteriorated due to a distortion.
If an output of the apparatus is continued without maintaining the vibration amplitude of the ultrasonic vibrator and probe at a constant level like the above example, the medical effect may drop. As a medical apparatus, the safety for an operator and patient must be considered by eliminating a possibility of ambustion and electric shock.
To solve the above described problem, Japanese Examined Patent Application No. 2604852 has disclosed a method for preventing a control voltage of the voltage control amplifier (hereinafter referred to as VCA) for changing an amplification factor of an oscillator output to make the drive current constant, from increasing abnormally due to a remarkable change in the electrical characteristic of the ultrasonic vibrator.
However, the above patent has only disclosed a restriction of a upper limit of the amplification factor of the VCA, but has not specified an appropriate range enabling the constant current control and PLL control by considering both those remarkable rise and drop of the impedance of the ultrasonic vibrator.